It is estimated that a fifth of all fresh water ponds, lakes and rivers in Florida is infested with Hydrilla verticillata L. F. Royle (Hydrocharitaceae), and the weed is spreading rapidly. Since its introduction into Florida waters around 1960, this weed has moved to several other states in the U.S.A. Serious economic losses and ecologic damages resulting from this submerged weed have spurred research on biological, chemical and mechanical controls. Among biological agents researched are plant pathogens; however, very few diseases of submerged weeds are known and those found on Hydrilla have not been sufficiently damaging or specific to this host to promote their use in the field.
In 1974, a disease of Stratiotes aloides L. (Hydrocharitaceae) in Holland was noted in which mature plants had symptoms of root- and crown-rots and severely diseased plants appeared to sink gradually as a consequence of tissue decay. A few infected plant parts were studied and a group of fungi were cultured from the plants including a Fusarium roseum "Culmorum" (Lk. ex Fr.) Synd. & Hans. In view of the close taxonomic relationship between Stratiotes aloides and Hydrilla verticillata it was considered that these fungi might be effective on Hydrilla verticillata. Among the many fungal isolates obtained from S. aloides, only "Culmorum" was capable of killing Hydrilla. Results prove that the Dutch "Culmorum" is a virulent pathogen of Hydrilla unlike most other fusaria tested on this host, and that it is effective in the control of Hydrilla in Florida.